Steel pipe is commonly used in the oil and gas industry. This type of pipe may be used in the transport of fluids to or from the well such as oil and gas gathering lines, flow lines, and fluid and gas injection lines which may be installed on the surface or buried. Steel pipe may also be used for downhole applications such as drilling, intervention, or production including drill strings, coiled tubing, production tubing, casing, and velocity and heater strings, and the like. Steel pipelines, gathering lines or injection lines are usually installed using short (30-40 foot) sections. This requires additional labor and provides the possibility for fluid leakage at each fitting. Such labor intensive installation may also lead to lost revenues if production or transport of the fluids is suspended during the installation.
To resist internal corrosion, steel alloys, non-metallic internal coatings, or fiberglass-reinforced epoxy pipe may be used, but all may still have the disadvantage of being sectional products. In addition, the wall of a fiberglass-reinforced epoxy pipe may be fairly damage intolerant and may requires careful handling, installation, and/or use of specific back-fill materials. Damage or cracks in the fiberglass reinforced epoxy layer can in some cases lead to small leaks or “weeping” of the pipe under pressure. In some applications, thermoplastic liners may be used as corrosion protection inside steel pipe, but these liners are susceptible to collapse by permeating gases trapped in the annulus between the liner and the steel pipe if the pressure of the bore is rapidly decreased. Unreinforced thermoplastic pipe, on the other hand, can usually only tolerate relatively low pressures especially at temperature and in the presence of oilfield fluids.
Fiberglass reinforced epoxy tubes used in oil and gas applications may have positive buoyancy, and thus may float, move, or otherwise have instability when in muddy, sandy or flooded ground unless weighted down. While in some situations positive buoyancy may be desirable, positive buoyancy can affect the performance of the tube and can also lead to an increase in damage from movement of the pipe in ground. Problems associated with positive buoyancy may be particularly acute with tubes that are manufactured from low-density structural materials or have large volumes of bore relative to the volume and density of the structural material.
Therefore, there is a need for a weighted, low-cost, corrosion resistant, spoolable, reinforced inner-lined pipe for such relatively low pressure applications so that the tube remains negatively buoyant when in use.